The invention concerns an ultrasonic transducer in the shape of an electrical capacitor formed of a counter-electrode and a film lying thereon, of synthetic material, metallised on one side and held by a clamping ring.
Such ultrasonic transducers are known and are very frequently used for running time measurements in flow field examinations in wind tunnels. They display a relatively large housing and require extensive mountings and special current feeds. The appreciable spatial extent of such an ultrasonic transducer and the associated auxiliary equipments frequently leads to disturbances in the wind tunnel, which make the measurement results unusuable. Beyond that, for the measurement of a flow field, several successive measurements must be performed, between which the ultrasonic transducer must be displaced. In this manner, merely stationary flows or such non-stationary processes let themselves be examined, in which the measurement operation can always be triggered at the respectively correct instant due to knowledge of the expected temporal course of the flow process (for example in the special case of periodicity). In that case, relatively long measuring times must be accepted. The possibilities of application of such an ultrasonic transducer are accordingly greatly restricted to special cases.